SAN FRANCISCO – Shares of IBM Corp. jumped Thursday after the technology company’s surprise announcement that it was still plenty prosperous in the third quarter despite the worsening economic climate.

The Armonk, N.Y.-based company released its results more than a week ahead of schedule Wednesday to help stop a steep slide in its stock price and to offer some perspective to the broader market. IBM is a component of the Dow Jones industrial average.

IBM’s profit beat Wall Street’s forecast by 4 cents per share and the company reaffirmed its full-year earnings guidance. Both were strong signs that IBM’s core businesses are holding up well despite the deteriorating U.S. economy and IBM’s large customer base in the crippled financial services industry.

Sales were short of analysts’ estimates by more than $1 billion, but the average estimate likely would have been lower by the planned Oct. 16 announcement because many analysts had started cutting their forecasts.

After running up steadily the first half of the year, IBM shares started sliding this summer and dropped precipitously in the last week. But after the unexpected earnings announcement, IBM stock was up $4.40, 4.9 percent, at $94.95 in morning trading Thursday.

IBM said it earned $2.05 per share in the July-September period, beating the $2.09 forecast of analysts polled by Thomson Reuters. Net income for the period was $2.8 billion, an increase of 20 percent over the same period last year.

Analysts were expecting sales of $26.5 billion, but analysts had started lowering their estimates before Wednesday’s earnings release. They cited the economy and a strengthening U.S. dollar as reasons for cutting their forecasts.

A strengthening greenback makes deals done in other currencies worth less when IBM accounts for the sales in dollars.

IBM maintained its forecast of at least $8.75 per share in profit in 2008, a 22 percent improvement over last year.

The results reassured analysts who had been looking for reverberations from a slowdown in corporate spending. Earlier in the week, business software maker SAP AG said its sales plunged at the end of September as global financial turmoil escalated.

Peter Misek, an analyst with Canaccord Adams, said the IBM results offered “relief.”

“That’s why the stock’s rallying,” he said. “It seemed like a global freeze happened in late September and extended, so it’s nice to see the biggest companies are still dealing with the biggest of their suppliers … the markets are still moving along, demand is still there.”